docs(env): Add audit logging configuration with realistic volume estimates

Add comprehensive audit logging section to .env.example with:
- Corrected database load estimates for various user scales
- Clear distinction between Sentry (errors) vs audit logs (compliance)
- When to enable: enterprise/compliance requirements
- Expected DB inserts: 50-100/day per 100 users (scales linearly)

Realistic estimates for 20k users:
- ~10,000-15,000 audit log inserts per day
- Events: registration, login, role changes, org membership, failures
- NOT "10-20 queries" - that was an underestimate

🤖 Generated with Claude Code
https://claude.com/claude-code

Co-Authored-By: Claude <noreply@anthropic.com>

Author: mjunaidca

auth-server/.env.example

@@ -123,6 +123,40 @@ NEXT_PUBLIC_CONTINUE_URL=http://localhost:3000
 # Example: AYasASQgxxx...
 # REDIS_TOKEN=
 
+# ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+# 📋 Audit Logging (OPTIONAL - Enterprise/Compliance)
+# ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
+# Audit logging tracks security-critical events for compliance (SOC2, ISO 27001, GDPR)
+# Different from error monitoring (Sentry) - audit logs are for investigations
+#
+# When to enable:
+#   ✅ Enterprise B2B customers (compliance requirement)
+#   ✅ SOC2, ISO 27001, HIPAA, GDPR compliance needed
+#   ✅ Security investigations and forensics required
+#   ❌ Early-stage products (adds DB load)
+#   ❌ Consumer apps without compliance requirements
+#
+# Expected Database Load:
+#   100 users:     ~50-100 inserts/day
+#   1,000 users:   ~500-700 inserts/day
+#   10,000 users:  ~5,000-7,000 inserts/day
+#   20,000 users:  ~10,000-15,000 inserts/day
+#
+# Events logged (5 critical actions only):
+#   - User registration (user.created)
+#   - Login events (session.created)
+#   - Role changes (role.updated)
+#   - Organization membership changes (member.added, member.removed)
+#   - Failed login attempts (captured by rate limiting)
+#
+# Note: This is separate from Sentry (error monitoring)
+#   - Sentry: Track exceptions, crashes, performance issues
+#   - Audit Logs: Track user actions for compliance and investigations
+#   - Both should be used together in production
+#
+# Enable audit logging (set to "true" to enable)
+# ENABLE_AUDIT_LOGGING=false
+
 # ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━
 # 🔐 OAuth Client Management
 # ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━